Many deaf or severely hearing-impaired individuals can understand speech in quiet environments using a cochlear implant (CI), which stimulates the auditory nerve directly with electrical current. However, their speech understanding typically declines significantly in even small amounts of background noise. For those who have some residual low-frequency hearing, the combination of electric and acoustic stimulation (EAS) can significantly improve speech understanding in background noise. Fundamental frequency (F0) variation and low-frequency amplitude envelope of the target talker are important cues for EAS benefit. The broad long-term goals of the proposed research are to advance the understanding of how low-frequency acoustic stimulation combines with electric stimulation to enhance speech understanding in difficult listening situations, and to enhance EAS benefit for individuals who might otherwise receive limited or no benefit. One long-term goal is to develop a wearable real-time processor that can deliver low-frequency speech cues to CI users more effectively. The specific aims are to (1) to increase the amount of EAS benefit to CI patients who already show a benefit; (2) To provide EAS benefit other CI patients who show little or no benefit typically; and (3) understand why some CI patients do not benefit from EAS, even when their audiometric results suggest they might. This work has the potential to extend the benefits of EAS to those CI users who do not possess enough residual hearing to show an EAS benefit typically, and to enhance the EAS benefit for those who do.